1. Field of the Invention
This invention relates generally to heat exchangers for refrigerant circuits and, more particularly, to a laminated type evaporator for an automotive air conditioning refrigerant circuit.
2. Description of the Prior Art
A laminated type evaporator is known in the prior art, as for example, Japanese Patent Application Publication No. 62-5097 which discloses an evaporator as shown in FIGS. 1-3. The evaporator 10 includes a plurality of tube units 11 of aluminum alloy each of which includes a pair of tray-shaped plates 12. Tray-shaped plates 12 include a shallow depression 120 defined therein, a flange 13 formed around the periphery thereof, and a narrow wall 14 formed in the central region thereof. Narrow wall 14 extends downwardly from an upper end of plate 12 and terminates approximately one-eighth the length of plate 12 away from the lower end thereof. Narrow wall 14 includes a flat top surface 14a. A plurality of diagonally disposed semicylindrical projections 15 project from the inner bottom surface of shallow depression 120. Semicylindrical projections 15 are aligned with one another in each of a plurality of, for example, four rows. As shown in FIG. 2, there are two rows of semicylindrical projections 15 located in shallow depression 120 on the right side of narrow wall 14 and two rows located on the left side thereof. Semicylindrical projections 15 also include a ridge 15a and are utilized in order to reinforce the mechanical strength of plate 12. A pair of cylindroid-shaped bulged portions 16 are formed in the upper region of plate 12 and project oppositely to semicylindrical projections 15 such that a hollow space 16b is defined by each bulged portion 16. An oval opening 16a is formed in the bottom surface of each bulged portion 16. A plurality of rectangular parallelepiped projections 17 project from the inner bottom surface of shallow depression 120 adjacent to the interior surface of each bulged portion 16. Each of the three rectangular parallelepiped projections 17 shown includes a flat top surface 17a. A rectangular flange 18 projects from the lower end of plate 12 in a direction opposite to semicylindrical projections 15, and is bent downwardly in a generally right angle at the terminal end thereof.
The levels of flat top surface 14a of narrow wall 14, ridge 15a of semicylindrical projections 15, and flat top surface 17a of parallelepiped projections 17 are even with the surface of flange 13. Therefore, when the pair of tray-shaped plates 12 are joined together by flanges 13 so as to form a passage 19 therebetween, narrow walls 14 of each plate 12 contact one another at the flat top surfaces 14a, parallelepiped projections 17 of each plate 12 contact one another at their flat top surfaces 17a, and semicylindrical projections 15 of plates 12 contact one another at the intersections 15b along ridges 15a. Flanges 13 of plates 12 are fixedly attached to each other by, for example, brazing or any other conventional manner, and flat top surfaces 14a of narrow walls 14 in plates 12 are also fixedly attached to each other by brazing, or on a like manner.
Evaporator 10 is formed by laminating together a plurality of tube units 11 and inserting corrugated fins 20 within the intervening space 21 between the adjacent tube units 11. Tube unit 11, located on the far left side of evaporator 10 shown in FIG. 1, includes a tray-shaped plate 12a having no bulged portion 16. Plate 12a is provided with a cylindroid-shaped tank 31 which is fixedly attached to the upper end thereof. The interior region of tank 31 is linked to hollow space 16b in the adjacent front side bulged portion 16 of plate 12 through an opening (not shown) formed in the upper end of plate 12a. Tube unit 11, located on the far right side of evaporator 10, also includes a tray-shaped plate 12b having no bulged portion 16. Plate 12b is provided with a cylindroid-shaped tank 32 which is fixedly attached to the upper end thereof. The interior region of tank 32 is similarly linked to hollow space 16b in the adjacent front side bulged portion 16 of plate 12 through an opening (not shown) formed in the upper end of plate 12b. Tank 31 is provided with a circular opening 31a formed in the front surface thereof. Tank 32 is provided with a circular opening 32a also formed in the front surface thereof. One end of an inlet pipe 50 is connected to opening 31a of tank 31 and one end of an outlet pipe 60 is connected to opening 32a of tank 32. Inlet pipe 50 is provided with a union joint 50a at the other end thereof and outlet pipe 60 is similarly provided with a union joint 60a at the other end thereof. A pair of side plates 22 are attached to the left side of plate 12a and to the right side of plate 12b, respectively, and corrugated fins 20 are disposed between side plate 22 and plate 12a, and between side plate 22 and plate 12b, respectively. The lower end of side plate 22 includes a rectangular flange 22a projecting inwardly and then bent downwardly in a generally right angle at the terminal end thereof. Respective tube units 11, corrugated fins 20, and side plates 22 are fixedly attached to one another by any conventional manner, such as brazing, for example. Although corrugated fins 20 are only illustrated in FIG. 1 at the upper and lower ends of intervening spaces 21, it should be understood that corrugated fins 20 continuously extend along the entire length of intervening spaces 21. In addition, although tray-shaped plate 12c located in the central region of evaporator 10 includes a pair of bulged portions 16, it should be noted that bulged portion 16 located on the front side of the evaporator does not have an oval opening 16a.
Latitudinally adjacent hollow spaces 16b of a pair of bulged portions 16 are linked to one another through oval openings 16a, thereby forming a pair of parallel conduits 30 and 40. Conduit 30 is located on the front side of evaporator 10 and conduit 40 is located on the rear side of evaporator 10. Conduit 30 is divided into left and right side sections 30a and 30b by plate 12c as shown in FIG. 1.
Referring also to FIG. 4, in the above-mentioned construction of the evaporator, when an automotive air conditioning refrigerant circuit operates, the refrigerant flows from the condenser (not shown) of the refrigerant circuit via a throttling device, such as an expansion valve, into the interior region of tank 31 through inlet pipe 50. The refrigerant in the interior region of tank 31 flows through left side section 30a of conduit 30 from the left side to the right side and concurrently flows into the upper right region of passage 19 of each of tube units 11. As shown in FIG. 2, the refrigerant in the upper right region of passage 19 then flows downwardly to the lower right region of passageway 19 in a complex flow path substantially formed from both diagonal and straight flow paths, as shown by the solid arrows in FIG. 2, while also exchanging heat with the air passing along corrugated fins 20. This complex flow path of the refrigerant enhances the heat exchangeability between the air and the refrigerant. The air passes through evaporator 10 from the front to the rear, as shown by the large narrow "A" in FIG. 4. The refrigerant located in the lower right region of passage 19 is turned at the terminal end of narrow wall 14 and directed to flow from the right side to the left side of passage 19 as shown by the solid arrows in FIG. 2. That is, the refrigerant flows from the front to the rear of passage 19, then flows upwardly to the upper left region of passage 19 in the complex flow path mentioned above while further exchanging heat with the air passing along corrugated fins 20, and finally, flows out of passage 19 of each of tube units 11. The refrigerant flowing out of passage 19 of each of tube units 11 combines together in conduit 40 and flows through conduit 40 from the left side to the right side thereof.
The refrigerant flowing through conduit 40, after passing through plate 12c, concurrently flows into the upper left region of passage 19 of each of tube units 11. The refrigerant in the upper left region of passage 19 then flows downwardly to the lower left region of passageway 19 in a complex flow path, like the aforementioned flow path, while exchanging heat with the air passing along corrugated fins 20. The refrigerant located in the lower left region of passage 19 is directed, at the terminal end of narrow wall 14, from the left side to the right side of passage 19. That is, the refrigerant flows from the rear to the front of passage 19, then flows upwardly to the upper right region of passage 19 in a complex flow path while further exchanging heat with the air passing along corrugated fins 20, and finally flows out of passage 19 of each of tube units 11. The refrigerant flowing out of passage 19 of each of tube units 11 combines together in the right side section 30b of conduit 30, and flows through the right side section 30b of conduit 30 from the left side to the right side thereof. The gaseous phase refrigerant located in the far right side of right side section 30b of conduit 30 flows into the interior region of tank 32 and then through outlet pipe 60 to the suction chamber of the compressor (not shown) of the refrigerant circuit.
In this prior art evaporator, the manufacturing process for plate 12 includes a drawing process for forming shallow depression 120, semicylindrical projections 15, parallelepiped projections 17 and bulged portions 16 from a rectangular sheet of aluminum alloy, and a punching process for punching out oval opening 16a from the bottom surface of each bulged portion 16. In the drawing process, shallow depression 120, semicylindrical projections 15, parallelepiped projections 17 and bulged portions 16 are formed by a plurality of drawing steps. The number of drawing steps required to form bulged portions 16 is greater than the number of drawing steps for forming the other above-mentioned elements because bulged portions 16 are more deeply and sharply depressed than the other elements. Therefore, the manufacturing of plate 12 becomes a complicated process. Furthermore, the large number of drawing steps necessary to form bulged portions 16 decreases the thickness of the aluminum alloy sheet at that point such that bulged portions 16 may be easily cracked in the drawing process. The cracking of bulged portions 16 must then be prevented by increasing the thickness of the rectangular sheet. However, this in turn unnecessarily increases the weight of plate 12, thus causing an unnecessary increase in the weight of evaporator 10, and unnecessarily decreasing the heat exchangeability of evaporator 10.